The invention relates to adjuvanted vaccine formulations, in particular influenza vaccines capable of mounting a mucosal immune response e.g. upon intranasal or intramuscular delivery.
Seasonal influenza is still one of the major causes for mortality and morbidity worldwide. Annual vaccinations are the most effective strategy to prevent and control influenza infections. Seasonal influenza vaccines are prepared based on the prediction of the expected strain of epidemic of the next season. These are parenterally injected vaccines that do not prevent the infection itself, which would reduce the severity and complications after the infection. Parenteral vaccines can induce the neutralizing IgG antibody in the serum but they cannot induce the secretory IgA antibody which acts on the mucosal surface. In contrast, intranasal (i.n.) vaccines may induce both a systemic and mucosal immune response. Secretory IgA antibodies on the mucosal membrane surface are highly effective for preventing infection because they react on the surface of the mucosal membrane before the pathogens attach to the epithelial cell surface, which is the first target of influenza viral infection. Moreover, serum IgG antibodies are less effective against drifted viral strains because they act more specifically than secretory IgA antibodies. Secretory IgA antibodies have cross-protective effects against variant strains of the influenza virus. The exact mechanism of the cross-reactive effects of IgA is still unknown, but this phenomenon is a great advantage in preventing infection. Influenza displays an extraordinary capacity to change the antigenic characteristics of its two major membrane proteins, hemagglutinin (HA) and neuraminidase (NA). This occurs by the continuous selection away from the adaptive immune response established in the human population. Due to the high mutation rate of the virus, a particular vaccine formulation usually works for only about a year. The World Health Organization coordinates the contents of the vaccine each year to contain the most likely strains of the virus to attack the next year. Nowadays, conventional vaccines are vaccines consisting of three inactivated influenza viruses (two A-strains and one B). This trivalent influenza vaccine is re-formulated annually, based on influenza strains projected by the WHO to be prevalent in the upcoming flu season. For example, the annually updated trivalent flu vaccine for the 2007-2008 season consists of hemagglutinin (HA) surface glycoprotein components from influenza H3N2, H1N1, and B influenza viruses.
Other advantages of i.n. delivery of vaccines is that delivery of the vaccine does not require trained health care personnel for the administration of vaccine, rendering this type of vaccines suitable for people with needle-phobia and circumvents the problem of needle stick injuries. Furthermore, it is reported that the mucosal immune system develops early in life and is not affected by aging (McElhaney J E. Vaccine 2005 Jul. 8; 23 Suppl 1:S10-25; Szewczuk M R et al. Ann N Y Acad Sci 1983 Jun. 30; 409:333-44). Therefore, a concomitant advantage of e.g. intranasal influenza immunization is that it can potentially provide effective immunity in all age groups and can be used for mass vaccination. Various concepts for immunization against influenza via the nasal or oropharyngeal route and using inactivated influenza antigen have been explored as needle-less alternatives to the subcutaneous or intramuscular immunization. Experimental data supportive for needle-less approaches have been generated in animal models. Concepts using inactivated influenza antigen (such as chemically inactivated whole virus particles, or further processed viral components such as split virus, or purified surface antigens haemagglutinin (HA) and/or neuraminidase (NA)) for immunization via the intranasal route that are supported by animal data include either the use of an adjuvant or immune stimulator in combination with the inactivated influenza antigen, or require multiple vaccination. An adjuvant is any substance that enhances the immunogenicity of antigens mixed with it. In humans successful vaccination against influenza via the intranasal route has only been reported for (a) live (cold adapted strains) influenza vaccines (FluMist™, MedImmune Vaccines Inc), (b) virosomal influenza vaccine adjuvanted with the heat labile toxin of E. coli (NasalFlu, Berna Biotech Ltd) or (c) using high amounts of antigen and repeated vaccination. Although live vaccines are capable of inducing a satisfactory immune response, their specific nature of being a live virus causes additional safety concerns, and is likely to induce side effects due to the required viral replication round in the upper respiratory tract. Also the required storage conditions are limiting the commercialization of these products. A strong association between the use of the intranasal influenza vaccine with E. coli HLT as adjuvant, and facial paralysis (Bell's Palsy), led to withdrawal of the HLT adjuvanted virosomal vaccine from the market.
Currently, live attenuated influenza virus vaccines (LAIV) are marketed for i.n. administration. LAIV vaccines have shown to induce both systemic and mucosal immune response. However, LAIV vaccine is licensed by the FDA only for persons aged 2-49 years and not for use in high risk populations (elderly, children and chronically ill patients) (Centers for Disease Control and Prevention. http://www.cdc.gov/flu/professionals/vaccination/pdf/targetpopchart.pdf; Belshe R B et al. Vaccine 2008 Sep. 12; 26 Suppl 4:D10-6). However, most of the marketed influenza vaccines are inactivated vaccines which can be administered safely via i.n. route to the whole population. A disadvantage of these vaccines is that they have shown to be poorly immunogenic when administered via this route (Vaccine 2007 Jul. 20; 25 (29):5367-73; Eyles et al., BioDrugs 2000 January; 13(1):35-59).
To increase the immunogenicity, inactivated influenza vaccines require adjuvants to potentiate the immune response when administered via the i.n. route. Several adjuvants are currently under development for i.n. immunizations like virus like particles (Matassov D et al. Viral Immunol 2007 September; 20(3):441-52), ISCOMS (Sjolander S et al. Vaccine 2001 Jul. 16; 19(28-29):4072-80), lipids, nucleic acids (Joseph et al. Vaccine 2006 May 1; 24(18):3990-4006) and bacterial components (Haan et al. Vaccine 2001 Apr. 6; 19(20-22):2898-907; Plante et al. Vaccine 2001 Oct. 12; 20(1-2):218-25). However, the development of many of these adjuvants systems is hampered by safety and regulatory concerns. For example potent bacterial adjuvants like LT (heat liable toxin of E. coli) have shown severe side effects in humans (Mutsch et al. N Engl J Med 2004 Feb. 26; 350(9):896-903). The inclusion of aluminium salt adjuvants as has been suggested for influenza vaccines not only requires extra mixing steps during manufacture, thereby slowing down overall manufacture, but inclusion of these salts is associated with various problems. For example, their insolubility means that adsorbed antigens settle from suspension, so preparation of individual doses from bulk vaccine requires extra care. In addition, binding of antigen to the salts complicates quality control of the final vaccines. In particular, some potency tests for influenza vaccines are based on in vitro immunoassays that require unbound antigen i.e. adsorption to the adjuvant means that these tests cannot be used. Recently, much emphasis is put on the phenotype of the immune response i.e. Th1, Th2 or balanced response. Subunit vaccine administered via the i.n. route and many of the nasal adjuvants like chitosan, ISCOMS, lipids, and LT induce a mixed Th1/Th2 type response. However, a Th1 response is considered to be superior to Th2 or a mixed response because it 1) results in better protection from infection; and 2) helps in virus neutralization by secretion of INF-γ. Moreover, the natural infection also induces a Th1 type of response. In addition, secretory IgA antibodies on the mucosal membrane surface are highly effective for preventing infection and, importantly, secretory IgA antibodies have cross-protective effects against variant strains of the influenza virus and the mucosal immune system develops early in life and is not affected by aging.
Thus, there is a clear need for an adjuvant which is potent, safe for human use and that can easily be approved by regulatory agencies. Preferably, a vaccine capable of inducing a mucosal immune response like secretory IgA antibodies and/or a response skewed towards Th1 type immunity is desirable. It is therefore an object of the invention to provide further and improved adjuvanted influenza vaccines (for both pandemic and interpandemic use), preferably a vaccine being suitable for intranasal and/or intramuscular delivery. A further aim is to provide a flexible method for influenza vaccine preparation that allows for a convenient and cost-effective annual re-formulation.